Are there two different races of Engineer?

It is possible that we are shown the Engineers seeding another world. For one, simple forms of life, according to some scientist, have been around for 3-4 billion years. However, the Cambrian Explosion, where life began to take on more complex forms, happened around half-a-billion years ago. Again, if they were shown seeding earth, whether 4 billion years ago to start simple life, or 500 million years ago to "reseed" and stir the pot a bit, that's still a long time for them to have remained unchanged by evolution. Another thought on this - the world that is being seeded in the first scenes has no plant life that can be seen, so the atmosphere would have been rather primordial. Yet, the Engineer (along with the others in the deleted scenes) are walking around without pressure suits, breathing just fine. Another argument that they are genetically perfect (remember the zenomorph could also exist in the vacuum of space).